1. Technical Field
The present invention relates to a hole opener boring apparatus and method for using such and more particularly to an improved mounting structure for a hole opener that allows a greater number of cutters to be placed on the hole opener.
2. Description of Related Art
Hole openers are used when pipelines, cables, or culverts, for example, must be installed under surface barriers such as highways, buildings, waterways and other surface obstructions without disturbing the surface. Before a hole opener is used, a trench is opened on both sides of the barrier. A pilot bore is formed under the barrier. If the pilot bore is of insufficient diameter to install the pipeline, then the hole may be opened up using a hole opener. Next a boring head which is also referred to in the art as a reamer or hole opener, is used to enlarge the pilot bore. Generally, a guide is positioned on the advancing side of the boring head. The guide on the boring head is designed to engage the walls of the pilot bore and help steer the pipeline boring head while the pilot bore is being enlarged. Drilling fluids are also supplied to the boring operation through the drill stem in the pilot bore to produce a slurry which floats the drilled material out the end of the hole. After a hole is opened up using the hole opener, a section of the pipeline is either pushed or pulled lengthwise through the bore from one side of the barrier to the other. The pipeline may also be pulled through by the hole opener as the hole is being opened. The installed pipeline section may then be welded into place and tested.
Various types of reamers or hole openers have been disclosed in the prior art. One such opener has cone cutters which are mounted around the circumference of an axial shaft called a drill stem that is used to drive the hole opener. These cutters have been mounted by attaching plates perpendicular to the drill stem to which the cutters are then attached. The number of cutters that may be mounted to the drill stem using current methods is limited because of the tremendous forces placed on the cone cutters when in operation. The support structure attached to the drill stem must be sufficiently strong to prevent excessive breakage during a drilling operation.
Because of the limitations posed by the current support structures used to mount the cutters to the drill stem, the number of cone cutters that may be placed around the circumference of the boring head is limited. This limitation in the number of cutters varies depending on the diameter of the cutter. However, regardless of the diameter of the cutter, the structural methods used in the prior art severely limit the number of cutters allowed. Thus, the prior art tools are very rough in operation when used in hard material such as rock or hard gravel. The prior art tools also require much more power than would be required if more cutters could be added to the circumference of the tool. The prior art hole openers are analogous to a square wheel in that they are very rough in operation, and they tend to produce holes which are elongated or egg-shaped because of the rough operation. The rough operation also increases the likelihood that the cone cutters will break and be left in the hole. The removal of cone cutters from a prior art boring head after a drilling operation has proven to be very difficult and expensive because of the primitive attachment means that have been used.
Furthermore, the tools of the prior art could not be pushed backwards through the hole easily because the tools had a tendency to sink or grab along the edges of the holes due to the flat backs of the tools. The use of only four cones on prior art devices causes excessive friction between the tool and the walls of the hole making it even more difficult to push the tools back through the hole. Thus, it is virtually impossible to push prior art tools back through the hole in order to smooth the jagged edges inside the hole and mechanically push debris out of the hole. In order to produce a clean hole using prior art tools, the tool is pulled through very slowly while drilling fluids are liberally applied at the hole opener to produce a slurry that floats the debris out of the hole. Alternatively, a different tool may be attached to the drilling rig for pushing the debris out of the hole. However, this is very time consuming because of the time required in changing the tools and is more expensive because a separate tool is required.
Therefore, it would be desirable to provide a hole opener more analogous to a round wheel to reduce vibration and to reduce the size of the power supply required to operate the tool. A reduction in the size of the power supply would allow smaller boring machines to enter markets which were previously open only to larger drilling rigs. A support structure for the hole cutters is needed which will accommodate an increased number of cone cutters around the circumference of the boring head to provide a hole opener which operates smoothly. It is also desirable for the hole cutter to be capable of collecting cone cutters as they break off to avoid leaving the broken cone cutters in the hole and thereby reduce the expense of drilling operations. Furthermore, the cone cutters should be easily removable so that new or different styles or sizes of cone cutters may be installed between drilling operations. Finally, the hole cutter should be capable of being pushed back through the hole in order to provide an effective and efficient means for mechanically pushing the material out the end of the hole without requiring the insertion of a different tool.
The present invention provides a hole opener support structure which allows for a greater number of cone cutters to be attached to the hole opener. Increasing the number of cone cutters decreases the roughness of operation of the hole opener and produces a hole which is round rather than oblong or egg-shaped. Consequently, much less power is required to operate a hole opener of the same diameter than is required by the prior art tools. The support structure provided by the present invention uses a barrel which is attached to the drill stem to effectively increase the diameter of the drill stem so that additional cutters may be attached to the hole opener. Using the barrel structure, the structural integrity of the tool is not compromised, and a strong support structure for the cutters is provided. The tapered shape of the hole opener allows the hole opener to be easily pushed back through the hole to displace debris left behind the hole opener as the hole is being cut. Because debris may be mechanically displaced from the hole using the method of the present invention, much less drilling fluid is required to open a hole.
In one embodiment of the present invention, the barrel has openings in the front and back to allow drilling fluid and material to pass through the hole opener. The openings are such that broken cone cutters are deposited through the front openings and trapped in the barrel, thereby preventing the broken cone cutters from being left in the hole. Furthermore, the cone cutters may be easily removed from the barrel between drilling operations. This feature is provided by embedding a bolt in a groove within the cone cutter segment. The bolt is used to secure the segment to a pocket attached to the barrel. Because the bolt itself is replaceable, the life of the cone cutter segments are prolonged. This results in a very versatile tool in that the same hole opener may be used for boring various types of materials, and less time is required to change worn-out cone cutters.